In a communication network defined by IMS (IP Multimedia Subsystem), the session is initiated based on a protocol called SIP (Session Initiation Protocol), SDP (Session Description Protocol)-based session information is exchanged, and an RTP (Real Time Transport Protocol) packet is transmitted in a P2P (Peer To Peer) architecture. A progress of transition to NGN (Next Generation network) enables multifarious types of terminals to perform a plurality of communications in a SIP-based session. In this case, the communication network is equipped with a server called an AS (Application Server) which provides services on a variety of media.
In the communication network defined by the IMS, normally the SIP server called a CSCF (Call Session Control Function) manages the session status. In the communication network defined by the IMS in the present situation, there is not any specific proposal about a method by which the CSCF notifies the AS of the session status.
To be specific, important factors for realizing a service involving a session operation in an extension of an existing voice and sound service (e.g., VoIP (Voice over Internet Protocol)) are a “disclosure of existing session information” and a “session control authority transfer (session transfer)”. Hereafter a voice communication service including a meaning of transferring of sound may be called simply as voice service. The voice service provides a kind of telephone function. In the present situation, the AS has no method of knowing the information on the existing session established by the CSCF. It is therefore difficult to provide the service involving the session operation in the extension of the existing voice service (see FIG. 1).
In FIG. 1, a user U1 of a mobile terminal 1A telephones a user U2 of a mobile terminal 2A via the CSCF. At this time, a voice session (parent session) is established between the mobile terminals 1A and 2A via the CSCF. In this case, there has hitherto been no function of newly providing a multimedia service related to the voice session.
For example, the session for transmitting and receiving a picture through an intermediary of the AS could not be established by way of an extension of the parent session between the user U1 and the user U2. Moreover, new image terminals 1B, 2B could not be added by way of an extension of the voice session between the user U1 and the user U2. Namely, the communication using the image terminals 1B and 2B could not be established by way of the extension of the parent session while the AS intervenes in establishing the communication. The reason why so is that there is no method by which the AS knows the existing session information managed by the CSCF. Thus, it was not feasible to add the new service involving the session operation via the AS with respect to the existing voice session.
Herein, the parent session connotes a session established via the CSCF between the user U1 and the user U2. Further, a second session, in which the AS intervenes, configured in relation to the parent session is referred to as a child session (of which a status is termed child presence). Moreover, the session represents a combination of a couple of terminals connected in the P2P architecture, a status of the connection between these terminals, or a flow of data transmitted and received via the connection between the terminals.
FIG. 2 illustrates a general method of providing the session information to the AS in a CSCF-based control method. For instance, a service for providing information on a telephone directory currently exists at a Web site on the Internet. This service is that the terminal of the user U1 accesses the telephone directory at the Web site, thus acquiring a call recipient (SIP-URI (Uniform Resource Identifier) etc) of the user U2 as a communication partner. Then, the terminal of the user U1 requests the Web site to originate a call to the terminal of the user U2. Thereupon, the server providing the Web site transmits an instruction to the CSCF via the AS, and the call origination from the terminal of the user U1 to the call recipient is conducted. Thus, the intermediary of the specific server as in the case of the server providing the Web site on the Internet facilitates the linkup between the AS and the CSCF.
The current CSCF procedure does not, however, enable the AS to be easily notified of the information on the parent session.    [Patent document 1] Japanese Unexamined Patent Publication No. 2004-507946